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Geogr. Fis. Dinam. Quat. DOI 10.4461/GFDQ.2013.36.6 36 (2013), 81-94, 14 figg., 1 tab. KENNETH HEWITT (*) «THE GREAT LATERAL MORAINE», KARAKORAM HIMALAYA, INNER ASIA ABSTRACT: HEWITT K., «The Great Lateral Moraine», Karakoram ured by non-glacial processes. A paraglacial influence is also present, Himalaya, Inner Asia. (IT ISSN 0391-9838, 2013). mainly through glacially induced rock slope instabilities. These lead to large postglacial landslides blocking rivers or descending onto smaller Large moraines and related ice margin deposits, observed along the surviving glaciers. The interpretation offered is a challenge for existing ablation zones of Karakoram glaciers, have been grouped together as the views of late Quaternary developments. Great Lateral Moraine (GLM). It was formerly attributed to the Little Ice Age. Other studies propose a longer sequence beginning with late KEY WORDS: Lateral moraines and troughs, Ice-marginal ramps, Mo- Pleistocene glaciations. All investigations have assumed the GLM records raine-dammed glaciers, Breach-lobes, Surge-type glaciers, Rockslide-rock climate-driven glacier expansions. Evidence presented here challenges avalanches, Fragmented drainage systems, Intermontane sedimentation, this, and the idea of a single origin in time or process. Bualtar Glacier in Transglacial processes, Valley glacier landsystems, Karakoram Himalaya. the Hunza Basin, with a much-discussed GLM, introduces the complexi- ties involved. The glacier is surge-type, its fluctuations affected by large landslides onto the ice. Both have triggered depositional episodes out-of- phase with surrounding glaciers and climate variability. More decisive has INTRODUCTION been local base-level control by landslides downstream of Bualtar, espe- cially the late Holocene, Baltit-Sumayar landslide. Similar conditions are Along the ablation zones of many Karakoram glaciers shown to affect many, if not all, GLMs. No consistent relations were bare cliffs in old lateral deposits rise from the ice edge and found with glacier size, morphology or known patterns of advance, but culminate above in prominent lateral moraines. The largest many surge-type glaciers and landslides in glacier basins are involved. A pervasive influence has been blocking of the upper Indus streams by of these were formerly regarded as a single regional phe- large mass movements. To address these complex developments, valley nomenon and called the Great Lateral Moraine (GLM). glacier landsystems concepts are employed, especially as applied to de- Meiners (1998, p. 55) describes it as «… a very well- bris-covered glaciers. Some distinctive Karakoram variants are identified. marked and well-formed lateral, partly high moraine, which The regional environment seems not to produce a unique type, but a surrounds the glacier tongues». A more explicit German complete spectrum of valley glacier landsystems. Recent evidence of glaciers transitioning between landsystem types suggest how GLMs have term is Ufermoranen-Dammen [«embankment moraine developed and why interactions of glacial, fluvial, lacustrine and eolian dam (or barrier)»] (Wiche, 1961; Haserodt, 1989, p. 212). systems, are important. GLMs are distinguished as «transglacial landsys- There are usually substantial troughs between the lateral tems», developments in which glacial activity is disturbed and reconfig- moraines and valley sides - the «ablation valleys» of older literature (Visser & Visser-Hooft, 1935-1938; Hewitt, 1993). In them, heterogeneous and discontinuous deposits (*) Department of Geography and Environmental Studies, Research build up where avalanches, rock falls and debris flows Associate, Cold Regions Research Centre, Wilfrid Laurier University, Waterloo, Ontario, N2L 3Z9, Canada. E-mail: [email protected] come from the valley slopes, and where drainage is chan- The paper is dedicated to Prof. Monique Fort, to acknowledge her spe- neled or impounded (fig. 1). cial and outstanding contributions to the geomorphology of the High Asian In the 19th and early 20th centuries, glacier ice was mountains. She has been an inspiration in tackling problems of scale and commonly observed standing at or above the lateral complexity that distinguish the region; that require attention to its peculiar- ities, and thinking «outside the box» of predominantly Eurocentric ideas moraines, adding to them and shedding water and debris (Fort, 1987, 1995; Fort & Peulvast, 1995; Fort, 2000). Investigations at into valley side troughs. It is something rarely observed Bualtar Glacier were funded by the International Development Research since the 1920s except during glacier surges, making it Centre, Ottawa, Canada; Pakistan’s Water and Power Development Au- seem logical to identify the GLM with the Little Ice thority; and Wilfrid Laurier University’s Office of Research. Local residents Age (LIA). Some equated it specifically with the «1850 and mountain guides, especially Mr. Shaffi Ahmed of Nagar, gave invalu- able information and field assistance. I am indebted to two reviewers for moraines» in the European Alps. According to von Wiss- helpful comments, and Ms. P. Schaus for preparing the figures. mann (1959), «… in High Asia [generally] the moraines… 81 FIG. 1 - The GLM along the left flank, mid-ablation zone of Chogo Lungma Glacier. The marginal trough is to the left of the great lateral moraine. Active ice to the right is at a somewhat higher level, but below the GLM crest (photo: K.H., 2003). originate in the high stand glaciation at the middle of the lower tongue and for some 10 km up-valley are huge later- past [19th] century…». However, Kick (1989) challenged al moraines (fig. 2). Substantial slope, kame terrace, and this view of the «large moraine» at Chogo Lungma and other Karakoram glaciers and supported Mason’s (1930) view, that «… the majority of glaciers in the region were in a condition of maximum advance between about 1905 and 1915». Haserodt (1984, p. 83) argues, on the basis of tree ring data, for: «… a minimum age of the GLM of Bagrot [Glacier, near Gilgit] of 280 years… closer to the beginning of the “Little Ice Age” period…». However, since the mid- 1980s, most studies invoke several glacial expansions to explain these features, including some much earlier than the LIA (Schneider, 1969; Haserodt, 1989; Kick, 1989). While not using the term, Kalvoda (1992) attributes lateral margin deposits called GLM by others to events beginning in the late Pleistocene. All existing interpretations at least agree that the GLM records climate-driven glacier fluctuations. Evidence as- sembled here supports a diversity of origins, in time and process. Perhaps the term GLM should be abandoned. However, it identifies widespread, conspicuous ice-margin features in the region, is an important notion in the litera- ture and, in itself, does not imply a particular explanation. Here, the plural is used to reflect the variety of GLMs. Quotes are applied when citing other usage. An example introduces the conditions of interest. THE BUALTAR GLMS Bualtar Glacier in the Hunza Basin, sometimes called «Hopar Glacier», has an area of 115 km2 and a main ice stream 22 km long. It is largely avalanche-fed and drains northwards from a precipitous source zone below Diran FIG. 2 - Ablation zone of Bualtar Glacier looking downstream showing its GLMs (arrows), the associated valley side deposits, and steep cliffs to Peak (7,266 m) in the Rakaposhi Range. With a terminus the present ice edge. Ultar Peak (7,388 m) is in the top right background at 2,450 m, total basin relief is 4850 m. Surrounding the (photo: K.H., 1986). 82 lacustrine deposits fill valley side troughs. Similar GLM ing from the distinct advance of this glacier…». He adopts a features occur along the Barpu Glacier, which terminates much-expanded time frame, proposing that, «The highest beside Bualtar and was joined to it in the past (fig. 3). [moraines]… formed during the Hunza phase of glaciation in the upper Pleistocene». In a more recent paper, Kalvoda Existing studies and interpretations & Goudie (2007, pp. 112-115) assign the «huge walls of lateral moraines [close to Nagar village]…» to «… the last Bualtar and Barpu Glaciers appear in several influential advance of the valley glacier in the upper Pleistocene investigations of the «GLM» and related matters. Haserodt [62,000-68,000 years ago]» (p. 108 and 113). There are no (1984, p. 93) discussed the GLM at «Hoppar» and sketched actual age-determinations for GLM sediments or surfaces its cross-profile, placing the highest ice in the «17th, 18th or at Bualtar. Tree ages noted by Haserodt (1989), as earlier 19th c.». A later paper describes the features as «High Stand by Wiche (1958), were not supported by tree-ring or other moraines» of the LIA, defined by «300, 75-100, and 10-25 dating methods (Kick, 1989). Chronologies are based on year vegetation growth» (Haserodt, 1989, pp. 214-217). presumed morpho-stratigraphic relations and inferred ele- The same features are identified by Kalvoda (1992, vation and vertical relations to glaciations of the Hunza Plate XXVI/2, p. 189) as: «… Glacigenous sediments of the valley (Shroder & alii, 1993, p. 154; Owen, 2006, p. 15). lower part of the Bualtar valley-glacier tongue… Huge, in The state of the Bualtar GLMs in recent decades is af- some places up to 160 m high walls of lateral moraines dat- fected by erosion, or burial by wind-borne dust, and tram- FIG. 3 - Topographical map of Bualtar and Barpu Glacier basins showing the extent of the GLM complex and debris-covered ice. 83 pling by animals and humans. More important, the great cliffs in former glacial deposits are «erosion» features. They do not record actual ice contact surfaces or trim- lines of the highest, last, or any past glacier expansion, but an extended period of degrading of GLM deposits (fig. 4). In particular, large slump blocks continue to form and slide towards the glacier on the Hopar and Shishkin sides (MacDonald, 1989; Hewitt, 2009a). Erosion has removed over half the original sediment build-ups above existing ice levels. The original GLMs and Bualtar ice surfaces must have been tens of meters higher than today’s rem- nants, and closer to the valley center (fig.